Boris Johnson was elected London mayor at the beginning of May
Henley goes to the polls on Thursday, 26 June in the by-election to replace Tory MP and London mayor Boris Johnson.
The Conservatives moved the writ in the Commons for the contest in the Oxfordshire constituency where Mr Johnson had a 12,793 majority in 2005.
Oxfordshire councillor John Howell will be the Tory candidate.
Labour's candidate is Richard McKenzie, and the Lib Dems' is Stephen Kearney. The Greens have chosen Mark Stevenson and UKIP have selected Chris Adams.
It will be the first by-election since the Tories triumphed at Crewe and Nantwich last month and a major test for party leader David Cameron, MP for nearby Witney.
The Lib Dems were the nearest challengers at the 2005 election in what is one of the safest Conservative seats in the country.
Henley result General Election 2005: Johnson (Con) 24,894 (53.5%); Turner (Lib Dem) 12,101 (26.0%); Saeed (Lab) 6,862 (14.7%); Stevenson (Green) 1,518 (3.3%); Gray-Fisk (UKIP) 1,162 (2.5%).